Iron alloy catalyzed oxidative dehydrogenation

ABSTRACT

IRON ALLOYS ARE EXCELLENT OXIDATIVE DEHYDROGENEATION CATALYSTS. THEY ARE PARTICULARLY USEFURL BVECAUSE OF THEIR STRENGTH AND METALLIC PROPERTIES. SOME OF THESE CATALYSTS CAN BE USED TO BUILD REACTORS OR REACTOR LINERS, OTHERS CAN BE PREPARED AS SCREENS OR WIRE OR IN VARIOUS OTHER DESIRABLE SHAPES TO BE USED IN FIXED OR MOVING BED DEHYDROGENATION.

United States Patent 3,778,488 IRON ALLOY CATALYZED OXIDATIVE DEHYDROGENATION Louis J. Croce, Seabrook, Tex., and Laimonis Bajars,

Princeton, N.J., assignors to Petra-Tex Chemical Corporation, Houston, Tex. No Drawing. Filed Jan. 26, 1970, Ser. No. 5,920 Int. Cl. C07c /18 US. Cl. 260-680 E 7 Claims ABSTRACT OF THE DISCLOSURE Iron alloys are excellent oxidative dehydrogenation catalysts. They are particularly useful because of their strength and metallic properties. Some of these catalysts can be used to build reactors or reactor liners, others can be prepared as screens or wire or in various other desirable shapes to be used in fixed or moving bed dehydrogenation.

The present invention relates to the oxidative dehydrogenation of organic compounds over iron containing metal alloy catalysts. The term alloy as employed herein is used to describe a mixture with metallic properties composed of two or more elements of which at least one is a metal. Oxidative dehydrogenations employing iron compounds as catalysts are well known. U.S. Pats. 3,270,080; 3,284,536; 3,303,234; 3,303,235; 3,303,236; 3,303,238; 3,308,182; 3,324,195; 3,334,152; 3,342,890; 3,398,100 and 3,450,787 disclose such processes. Although excellent results have been obtained with many of the catalysts described in the prior art, it is an object of this invention to provide further improved catalysts. Another object is to improve the strength of the catalyst. These and other objects will become obvious from the following description of the invention.

An advantage of the present alloy catalysts over prior iron compound catalysts is the versatility of form in which the alloys can be used. For example, the reactor can be made or lined with the alloy catalyst; the catalyst can be prepared as mats, screens, wool or the like and loaded into the reactor; the catalyst can be formed in any desired shape and substantially any size, i.e., spheres, ovals, cubes, saddles, rings, etc.; or the catalysts can be formed with a leachable material which is removed leaving only the alloy in a porous form. Many of the present iron alloy catalysts have exceptional strength and can be employed in moving bed operations.

The process of this invention may be applied to the dehydrogenation of a wide variety of organic compounds. Such compounds normally will contain from 2 to 20 carbon atoms, at least one H H JHL grouping, a boiling point below about 350 C., and such compounds may contain other elements, in addition to carbon and hydrogen such as oxygen, halogens, nitrogen and sulfur. Preferred are compounds having 2 to 12 carbon atoms, and especially preferred are compounds of 3 to 6 or 8 carbon atoms.

Among the types of organic compounds which may be dehydrogenated by means of the process of this invention are nitriles, amines, alkyl halides, ethers, esters, aldehydes, ketones, alcohols, acids, alkyl aromatic compounds, alkyl heterocyclic compounds, cycloalkanes, alkanes, alkenes, and the like. Illustration of dehydrogenations include propionitrile to acrylonitrile; propionaldehyde to acrolein: ethyl chloride to vinyl chloride; methyl isobutvrate to methyl methacrylate; 2 or 3 chlorobutene-l or 2, 3 dichlorobutane to chloroprene; ethyl pyridine to vinyl pyrice idene; ethylbenzene to styrene; isopropylbenzene to a-methyl styrene; ethylcyclohexane to styrene; cyclohexane to benzene; ethane to ethylene or acetylene; propane to propylene, methyl acetylene, allene, or benzene; isobu tane to isobutylene; n-butane to butene and butadiene-l,3; n-butene to butadiene-1,3 and vinyl acetylene; methyl butene to isoprene; cyclopentane to cyclopentene and cyclopentadiene-1,3; n-octane to ethyl benzene and orthoxylene; monomethylheptanes to xylenes; ethyl acetate to vinyl acetate; 2,4,4-trimethylpentane to xylenes; and the like. This invention may be useful for the formation of new carbon to carbon bonds by the removal of hydrogen atoms such as the formation of a carbocyclic compound from two aliphatic hydrocarbon compounds or the formation of a dicyclic compound from a monocyclic compound having an acyclic group such as the-conversion of propene to diallyl. Representative materials which are dehydrogenated by the novel process of this invention include ethyl toluene, alkyl chlorobenzenes, ethyl naphthalene, isobutyronitrile, propyl chloride, isobutyl chloride, ethyl fluoride, ethyl bromide, n-pentyl iodide, ethyl dichloride, 1,3 dichlorobutane, 1,4 dichlorobutane, the chlorofluoroethanes, methyl pentane, methylethyl ketone, diethyl ketone, n-butyl alcohol, methyl propionate, and the like.

Suitable dehydrogenation reactions are the following: Acyclic compounds having 4 to 5 non-quaternary contiguous carbon atoms to the corresponding olefins, diolefins or acetylenes having the same number of carbon atoms; aliphatic hydrocarbons having 6 to 16 carbon atoms and at least one quaternary carbon atom to aromatic compounds, such as 2,4,4-trimethylpentene-1 to a mixture of xylenes; acyclic compounds having 6 to 16 carbon atoms and no quaternary carbon atoms to aromatic compounds such as n-hexenes to benzene; cycloparaifins and cycloolefins having 5 to 8 carbon atoms to the corresponding olefin, diolefin or aromatic compound, e.g., cyclohexane to cyclohexene or cyclohexadiene or benzene; aromatic compounds having 8 to 12 carbon atoms including one or two alkyl side chains of 2 to 3 carbon atoms to the corresponding aromatic with unsaturated side chain such as ethyl benzene to styrene.

The preferred compounds to be dehydrogenated are hydrocarbons with a particularly preferred class being acyclic non-quaternary hydrocarbons having 4 to 5 contiguous carbon atoms or ethyl benzene and the preferred products are n-butene-l or 2, butadiene-l,3, vinyl acetylene, 2-methyl-l-butene, 3-methyl-l-butene, 3-methyl-2 butene, isoprene, styrene or mixtures thereof. Especially preferred as feed are n-butene-l or 2 and the methyl butenes and mixtures thereof such as hydrocarbon mixtures containing these compounds in at least 50 mol percent.

The dehydrogenation reaction may be carried out at atmospheric pressure, superatmospheric pressure or at subatmospheric pressure. The total pressure of the system will normally be about or in excess of atmospheric pressure, although sub-atmospheric pressure may also desirably be used. Generally, the total pressure will be between about 4 p.s.i.a. and about or p.s.i.a. Preferably the total pressure will be less than about 75 p.s.i.a. and excellent results are obtained at about atmospheric pressure.

The organic compound to be dehydrogenated is contacted with oxygen in order for the oxygen to oxidatively dehydrogenate the compound. Oxygen may be fed to the reactor as pure oxygen, as air, as oxygen-enriched air, oxygen mixed with diluents, and so forth. Oxygen may also be added in increments to the dehydrogenation zone. Although determinations regarding the mechanism of reaction are difiicult, the process of this invention is an oxidative dehydrogenation process wherein the predominant mechanism of this invention is by the reaction of oxygen with the hydrogen released from the hydrocarbon.

The amount of oxygen employed may vary depending upon the desired result such as conversion selectivity and the number of hydrogen atoms being removed. Thus, to dehydrogenate butane to butene requires less oxygen than if the reaction proceeds to produce butadiene. Normally oxygen will be supplied (including all sources, e.g. air to the reactor) in the dehydrogenation zone in an amount from about 0.2 to 1.5, preferably 0.3 to 1.2, mols per mol of H being liberated from the organic compound. Ordinarily the mols of oxygen supplied will be in the range of from .2 to 2.0 mols per mol of organic compound to be dehydrogenated and for most dehydrogenations this will be within the range of .25 to 1.5 mols of oxygen per mol of organic compound.

Preferably, the reaction mixture contains a quantity of steam or diluent such as nitrogen with the range generally being between about 2 and 40 mols of steam per mol of organic compound to be dehydrogenated. Preferably, steam will be present in an amount from about 3 to 35 mols per mol of organic compound to be dehydrogenated and excellent results have been obtained within the range of about 5 to about 30 mols of steam per mol of organic compound to be dehydrogenated. The functions of the steam are several-fold, and the steam may not merely act as a diluent. Diluents generally may be used in the same quantities as specified for the steam. These gases serve also to reduce the partial pressure of the organic compound.

It is one of the advantages of this invention that halogen may also be present in the reaction gases to give excellent results. The presence of halogen in the dehydrogenation zone is particularly effective when the compound to be dehydrogenated is saturated, such as a saturated hydrocarbon. The halogen present in the dehydrogenation zone may be either elemental halogen or any compound of halogen which would liberate halogen under the conditions of reaction. Suitable sources of halogen are such as hydrogen iodide, hydrogen bromide and hydrogen chloride; aliphatic halides such as ethyl iodide, methyl bromide, methyl chloride, 1,2-dibromo ethane cyclo-aliphatic halides, ammonium iodide; ammonium bromide; ammonium chloride; sulfuryl chloride; metal halides including molten halides; and the like. The halogen may be liberated partially or entirely by a solid source as disclosed in the process of US. 3,130,241, issued Apr. 21, 1964. Mixtures of various sources of halogen may be used. The amount of halogen calculated as elemental halogen, may be as little as about 0.0001 or less mol of halogen per mol of the organic compound to be dehydrogenated to as high as 0.2 or 0.5.

The temperature for the dehydrogenation reaction generally will be at least about 250 C. such as greater than about 300 C. or 375 C. and the maximum temperature in the reactor may be about 700 C. or 800 C. or perhaps higher such as 900 C. under certain circumstances. However excellent results are obtained within the range of or about 350 C. to 700 C. such as from or about 400 C. to or about 675 C. The temperatures are measured at the maximum temperature in the dehydrogenation zone.

The gaseous reactants may be conducted through the reaction chamber at a fairly wide range of flow rates. The optimum flow rate will be dependent upon such variables as the temperature of reaction, pressure, particle size, and so forth. Desirable flow rates may be established by one skilled in the art. Generally the flow rates will be Within the range of about 0.10 to liquid volumes of the organic compound to be dehydrogenated per volume of dehydrogenation zone containing catalyst per hour (referred to as LHSV). Usually, the LHSV will be between 0.15 and about 5. For calculation, the volume of a fixed bed dehydrogenation zone containing catalyst is that original void volume of reactor space containing catalyst.

The catalysts of thisinvention contain iron and at least one other metallic element Me. The alloys of the present invention can be solid solutions of the substitutional or the interstitial type; dispersions or compounds. The iron and the second metal, Me of the solid solutions can be completely or partially soluble or essentially insoluble.

The quantity of iron in the alloy can vary greatly from a predominant amount, i.e., greater than for example 90-'99% to a small quantity, i.e., .1 or less. More generally the iron will be present in a range of 5.0 to 95.0% of the total components. The percents used herein are by weight unless otherwise indicated.

The second metal, Me, can have any chemical valence. Generally they will be diand trivalent metals. The crys tal structure is not critical, although the crystal structure of the components will determine the form of the alloy, i.e., solution, dispersion or compound. In addition to the second metal, Me, the alloy of the present invention can contain other metals.

In addition to iron the present alloy catalyst will contain metal or metals from Groups I-B, II-B, III-A, III-B, IV-B, V-A, V-B, VI-B, VII-B, VIII and the lanthanides and actinides, e.g., La, Ce, Pr, Nb, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa and U of the Periodic Table. Preferably alloy catalysts would be those containing 5.0 to 95.0% iron combined with at least one metal selected from the group consisting of Mg, Sr, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Al, Ge, Zr, Mo, Pd, Sn, W, Pt, Pb, Bi, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Ac, Th, Pa and mixtures thereof. A more preferred group of metals, Me, is selected from the groups consisting of Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Al, Zr, Mo, Pd, Sn, W, La, Ce and mixtures thereof. The alloy catalysts can contain some nonmetallic elements such as carbon, nitrogen, sulfur, phosphorus, chlorine, or bromine. If these additives are part of the alloy it is usually by an interstitial arrangement where the small radii of the additives are accommodated in the interstices of the lattice of a metal. Another means of modifying the alloy catalyst is by treatment before or during their use with organic or inorganic compounds of the nonmetallic materials, i.e., hydrochloric acid, sulfuric acid, nitric acid, chlorine, bromine, nitrogen, mercaptans, etc. Other modifiers that can improve catalyst efiiciency are silicon and boron.

The preparation of alloys is an old art and forms no part of the present invention. The alloys of the invention can be fabricated within the limits of the particular alloy by casting, sintering, hot working, cold working, joining, machining and the like. Those alloy catalysts of the present invention which contain a predominant amount of iron, i.e., steels, are among the most useful since they are easily worked and generally possess great strength.

Unless stated otherwise, the compositions referred to in this application are the main active constituents of the dehydrogenation process during dehydrogenation and any ratios and percentages refer to the surface of the catalyst in contact with the gaseous phase during dehydrogenation.

The catalysts of the present invention are preferably activated by treatment with strong acids such as concentrated nitric acid or concentrated sulfuric acid or strong bases such as NaOH. The acid treated alloys are dried and calcined to decompose the nitrates and sulfates that might have formed. The NaOH must be washed from alloy catalysts since it has a deactivating effect. In addition to treatment with strong acids or bases the alloy catalysts are usually calcined in a controlled atmosphere such as nitrogen, hydrogen, helium or air for five minutes to four hours at temperatures of 600 to 1300 C.

The process of this invention utilizes either a fixed bed or moving bed, such as a fluidized catalyst, reactor. Re-

1 See Handbook of Chemistry and Physics, 39th ed., 1957- 236 glfmical Rubber Publishing Co., Cleveland, Ohio, pp.

actors which have been used for the dehydrogenation of hydrocarbons by non-oxidative dehydrogenation are satis factory such as the reactors for the dehydrogenation of n-butene to butadiene-1,3. Although means to remove heat from the reactor may be employed, such as coils, the invention is particularly useful with essentially adiabatic reactors where heat removal is a problem.

The following examples are only illustrative of the invention and are not intended to limit the invention. All percentages are weight percent unless specified otherwise. All conversions, selectivities and yields are expressed in mol percent of the designated feed. The apparatus employed was a Vycor glass reactor.

EXAMPLE 1 An alloy containing 50 weight percent iron and 50 weight percent aluminum in 2-5 mM. chips was boiled in concentrated HNO evaporated to dryness and further heated (e.g. 700 C.) to decompose the nitrates. Butene-Z was oxidatively dehydrogenated under the conditions shown in Table I.

TABLE I Bu-2/02/ C/ /Y steam Reaction mole mole mp percent Run ratio d, LHSV butadiene EXAMPLE 2 50/50 iron:zinc alloy treated in the same manner as the catalyst of Example 1 (i.e., chips boiled in HNO etc.) gave C/S/Y of butene-Z to butadiene of 60/82/49 at LHSV of 0.6, 430 C. reaction temperature and mole ratio of butene-Zzsteamzoxygen of 1/ 0.7.

EXAMPLE 3 A catalyst of 50/50 wt. percent Fe/Al, 2-5 mesh chips was leached with a 25% sodium hydroxide solution, washed with distilled water, boiled with a solution of 0.1 m. Zn(NO +0.1 N HNO and the mixture evaporated to dryness. At 1 LHSV, butene-Z/ steam/ oxygen mole ratio of 1/15/0.6 at 450 C. the C/S/Y to butadiene was 60/92/55.

EXAMPLE 4 An iron/aluminum alloy (50/50 wt. percent) was pretreated in several difi'erent ways and used to oxidatively dehydrogenate butene-Z to butadiene. The conditions and results are shown in Table H.

washed tree of Na,- dried;

a flydrocarbon flow: 1 LHSV; hydrocarbonIoxygen/steam mole ratio Concentrated acids were used for the activations:

6 EXAMPLE 5 An ironzaluminum alloy (35/65 wt. percent) was boiled with concentrated HNO calcined at 700 C. for one hour, placed in the reactor and butene-2 oxidatively dehydrogenated at LHSV of 1, mole ratio butene-Z/oxygen/steam of 1/0.6/15 at 500 C. to give C/S/Y mole percent butadiene of 57/86/49.

The invention claimed is:

1. A process for the oxidative dehydrogenation of organic compounds in the presence of oxygen and a catalyst consisting essentially of an alloy containing from 5 to 95 percent by weight iron with the remainder consisting essentially of a metallic element selected from the group consisting of Cu, Zn, Al, Sn, and mixtures thereof, said organic compounds containing up to 12 carbon atoms and having 4 to 5 non-quaternary contiguous carbon atoms.

2. The process according to claim 1 wherein the alloy contains 35 to 50 weight percent iron and 50 to 65 weight percent aluminum.

3. The process according to claim 2 wherein the alloy is treated with a strong acid or base.

- 4. The process according to claim 3 wherein the alloy is treated by contacting a strong acid selected from the group consisting of H HNO and HBr, dried and then heated at a temperature in the range of 600 to 1300 C.

5. The process according to claim 4 wherein the organic compound is butene.

6. The process according to claim 1 wherein the alloy contains 50 weight percent iron and 50 weight percent of a member selected from the group consisting of aluminum and zinc.

7. The process according to claim 6 wherein the alloy is treated by contacting HNO dried and then heated at a temperature in the range of 600 to 1300 C.

References Cited UNITED STATES PATENTS 3,207,809 9/1965 Bajars 260680 3,207,811 9/1965 Bajars 260-680 1,972,013 8/1934 Forwood 252472 X 2,391,004 12/1945 Breuer 260681.5 3,308,198 3/ 1967 Bajars 260-68O 3,118,007 1/ 1964 Kronig et al 260-680 FOREIGN PATENTS 179,304 4/1966 U.'S.S.R. 260-680 1,102,420 2/ 1968 Great Britain 260-680 E PAUL M. COUGHLAN, J 11., Primary Examiner US. Cl. X.R. 

